The oil field drilling industry has found many uses for the hydrodynamically lubricated, ring shaped squeeze packing type rotary shaft seals embodying the principles set forth in U.S. Pat. No. 4,610,319 and marketed by Kalsi Engineering, Inc. of Sugarland, Tx. under the registered trademark, Kalsi Seals.RTM.. Hydrodynamically lubricated seals are used to provide lubricant retention and contaminant exclusion in harsh abrasive environments, such as the downhole oil field drilling environment, and have been successfully used in both low and high lubricant pressure installations. Present commercial oil field related applications include rotary cone rock bits, mud motors, high speed coring swivels, and rotating drilling heads. All references herein to hydrodynamically lubricated seals or hydrodynamic seals are directed to seals embodying the principles of the above identified U.S. Patent.
FIGS. 11-18 of this specification represent prior art hydrodynamic seals which are discussed herein to enhance the readers' understanding of the distinction between these prior art seals and the present invention. One of the first commercially implemented oil field related applications for the hydrodynamic rotary shaft seal is a low lubricant pressure application, the rotary cone drilling bit, which is exemplified in FIG. 11. The cross-sectional geometry of the rotary cone hydrodynamic drill bit seal is dictated by the shape, length and relative position of the shaft interface and by the relative position of the seal groove. This results in an dynamic contact geometry that is approximately centered relative to the static geometry of the seal. The drill bit seal defines a static sealing interface 1, an environmental side 2 for contact with the drilling fluid and a lubricant side 3 for contact with the lubricant in the lubricant chamber of the bit. The seal also forms a sharp exclusionary edge 4 and a dynamic sealing interface 5 which are in contact with the cylindrical sealing surface 6 of the shaft and forms a non-circular hydrodynamic edge 7 which is exposed to the lubricant. The laterally offset relationship of the planar surface 2 on the environmental or mud side of the seal and the sharp circular exclusionary edge 4 is dictated by the corner radius of the shaft 8. This feature causes the dynamic sealing interface of the drill bit seal to be substantially centered with respect to the static interface of the seal. Consequently, radial compression of the hydrodynamic rotary cone drill bit seal does not tend to induce twisting of the seal. Development of the cylindrical "footprint" of the dynamic sealing interface of the drill bit seal is shown in FIG. 13.